Differences between schematic and .xdc

[Kabs]

Hi All,

I am fairly new to FPGA (but not hardware), coming from a mainly software background.

I am developing within Vivado.

I am having problems identifying the correct pins for Pmod connectors on my Nexys A7.

There are differences between the circuit diagram and the .XDC file for the board. I am wondering which of the two to go by because I do not want to accidentally assign output to a pin which may cause problems if it was not meant to be assigned to. So far I have seen differences within JA and JB. most discrepancies are with JB

JB XDC & circuit diagram assignments.

XDC        Circuit        FPGA pin
B3            B4            H14
B4            B7            E16
B5            B8            F13
B6            B9            G13
B7            B3            G16

 

 

I would be grateful if someone knows which one to go for (now and the future).

Many thanks,

 

Stephen.

 

[JColvin]

Hi @Kabs,

Which version of the Nexys A7 are you looking at?

I'm comparing the schematic of the Nexys A7 (available here, https://digilent.com/reference/programmable-logic/nexys-a7/start#documentation, all of the pinouts each of the D.X revisions are the same) to the Nexys A7 .xdc file that is available on our Github (https://github.com/Digilent/digilent-xdc) and as far as I can tell each of the Pmod pins are matching which FPGA pin they are assigned to.

I've attached a screenshot (with added highlighting on the relevant Pmod pins from page 7 of the Nexys A7 schematic) as reference of what I am comparing to the pin assignments from the .xdc file (https://github.com/Digilent/digilent-xdc/blob/master/Nexys-A7-100T-Master.xdc#L84)

Thanks,
JColvin

[Kabs]

Hi JColvin,

Thanks for the response.

Unfortunately there is absolute disagreement between assignments on my board and XDC/circuit diagram versions.

By trial and error I have managed to place most of the pins for JA & JB as you see below paired with what the XDC/circuit says.

In cases where I haven't (yet) found verifiable values I have put a question mark. 

I have fully verified the ones I have marked.

I wonder, do I have a counterfeited board?, Are there such things?

 

 

[JColvin]

Hi @Kabs,

I apologize for the delay, it looks like your response was hidden for some reason. I'm also not able to view the image you attached for whatever reason (tried on Firefox, Chrome, and Edge).

Could you send me a picture of the board that you have? I briefly thought that maybe you had the Nexys A7 50T rather than the Nexys A7 100T which was making the difference, but when comparing the two .xdc files that Digilent has on our Github (50T, 100T) all the pin assignments are the same, indicating that the physical FPGA pins are also identical in layout.

As for the counterfeited board question, I'd certainly hope that is not the case; I have not personally heard of that happening to Digilent. But I would feel better about seeing your board (and the image you attempted to attach) so I can offer some better insight.

Thanks,
JColvin